The present invention relates to an image recording apparatus. More particularly, the invention relates to an exposure device for such an image recording apparatus.
Conventional exposure device for image recording apparatus generally includes an exposure unit, a light transmitting unit, and an image forming unit. In the exposure unit, a light is irradiated onto an original. In the light transmitting unit, the light reflected on or transmitted through the original is directed to a photosensitive recording medium through an optical system composed of reflector, filter, lens and the like. In the image forming unit, a latent image is formed on the photosensitive recording medium in accordance with the light transmitted by the light transmitting unit.
The sensitivity of such a photosensitive recording medium changes depending on the temperature of the recording medium per se. Provided that the intensity of light radiation for the photosensitive recording medium is constant, the sensitivity of the recording medium is lowered when the temperature of the recording medium is excessively high or low. The photosensitive recording medium shows a good sensitivity in a certain temperature range. Since the photosensitive recording medium is easily affected by ambient temperature such as a room temperature and the thermic rays irradiated from a light source, reproducibility of the image formed on the photosensitive recording medium is degraded and irregularity of the image formed thereon occurs.
The fluctuation of the intensity of the light radiation also causes to degrade reproducibility and to occur irregularity of the image formed on the recording medium. The amount of light radiated from a halogen lamp used as a light source is changes greatly when the voltage applied thereto slightly fluctuates. This is due to the fact that the intensity of the radiation light from the halogen lamp varies in proportion to third to fifth power of the voltage applied to the halogen lamp. Accordingly, the reproducibility of the image formed on the photosensitive recording medium is degraded even though the voltage applied to the light source is slightly fluctuated.
A prior art exposure device further causes poor reproducibility and irregularity of the image formed on the recording medium when photosensitive and pressure-sensitive recording sheet as disclosed in U.S. Pat. No. 4,399,209 is used. In such a device, the photosensitive recording medium intimately overlapped on the original are set on a plane support and a transparent plate is urged thereon with pressure, so that the photosensitive recording medium contacts the original. Light is radiated onto the photosensitive recording medium through a transparent plate and the original. If the surfaces of the plane support and the transparent plate are uneven, the pressure applied to the recording medium may locally become high. As a result, the microcapsule may be ruptured by this concentrated pressure, thus a fogging may occur in the reproduced copy.